Apparatus including a perpendicular magnetic recording layer having a convex magnetic anisotropy profile

ABSTRACT

An apparatus may include a first magnetic layer, a first exchange break layer formed on the first magnetic layer, a second magnetic layer formed on the first exchange break layer, a second exchange break layer formed on the second magnetic layer, and a third magnetic layer formed on the second exchange break layer. The first magnetic layer has a first magnetic anisotropy energy, H k1 , the second magnetic layer has a second magnetic anisotropy energy, H k2 , and the third magnetic layer has a third magnetic anisotropy energy, H k3 . In some embodiments, H k1 −H k2  is less than H k2 −H k3 . In some embodiments, the apparatus may be a perpendicular magnetic recording medium.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic diagram of a hard disc drive.

FIG. 2 is an example of a plot of magnetic anisotropy versus distancefrom hard layer for a magnetic recording layer comprising a continuouslygraded composition.

FIG. 3 is a schematic block diagram illustrating an example of arecording media stack including a recording layer comprising a firstmagnetic layer, a first exchange break layer, a second magnetic layer, asecond exchange break layer, and a third magnetic layer.

FIGS. 4A-4E are exemplary plots of magnetic anisotropy versus magneticlayer for a plurality of recording layers according to the presentdisclosure.

FIGS. 5A and 5B is a schematic block diagram illustrating an example ofa magnetic recording layer comprising n magnetic layers alternating withn−1 exchange break layers.

FIG. 6 is a flow diagram that illustrates an example of a technique forforming a magnetic recording layer.

FIGS. 7A and 7B are a switching coercivity contour map and a reductionin energy barrier contour map, respectively, for an example of amagnetic recording layer constructed according to the disclosure.

FIGS. 8A and 8B are a switching coercivity contour map and a reductionin energy barrier contour map, respectively, for an example of amagnetic recording layer constructed according to the disclosure.

FIGS. 9A and 9B are a switching coercivity contour map and a reductionin energy barrier contour map, respectively, for an example of amagnetic recording layer constructed according to the disclosure.

FIGS. 10A and 10B are a switching coercivity contour map and a reductionin energy barrier contour map, respectively, for an example of amagnetic recording layer constructed according to the disclosure.

DETAILED DESCRIPTION

FIG. 1 illustrates an example of a magnetic disc drive 10 including amagnetic recording medium according to one aspect of the presentdisclosure. Disc drive 10 includes base 12 and top cover 14, shownpartially cut away. Base 12 combines with top cover 14 to form thehousing 16 of disc drive 10. Disc drive 10 also includes one or morerotatable magnetic recording media 18. Magnetic recording media 18 areattached to spindle 24, which operates to rotate media 18 about acentral axis. Magnetic recording and read head 22 is adjacent tomagnetic recording media 18. Actuator arm 20 carries magnetic recordingand read head 22 for communication with magnetic recording media 18.

Magnetic recording media 18 store information as magnetically orientedbits in a magnetic recording layer. Magnetic read/write head 22 includesa recording (write) head that generates magnetic fields sufficient tomagnetize discrete domains of the magnetic recording layer on magneticrecording media 18. These patterns of domains of the magnetic recordinglayer represent the bits of data, with changes of the magneticorientation representing a “1.” A “0” is represented by a regioncomprising a constant magnetization for about twice the bit length.Magnetic recording and read head 22 also includes a read head that iscapable of detecting the magnetic fields of the discrete magneticdomains of the magnetic recording layer.

Perpendicular magnetic recording media are magnetic recording media 18with a perpendicular magnetic anisotropy field (H_(k)) in the magneticrecording layer and magnetization forming in a direction substantiallyperpendicular to the plane of the magnetic recording layer.Perpendicular magnetic recording media may be employed in magneticrecording systems. Perpendicular magnetic recording media may befabricated with polycrystalline CoCr or CoPt-oxide containing magneticrecording layers. Co-rich areas in the polycrystalline magneticrecording layer are ferromagnetic while Cr- or oxide-rich areas formproximate grain boundaries in the polycrystalline magnetic recordinglayer and are non-magnetic. Lateral magnetic exchange coupling betweenadjacent ferromagnetic grains is attenuated by the non-magnetic areas inbetween grains.

Progress in magnetic data storage devices, such as disc drive 10, comesprimarily through increasing the storage capacity of the device, i.e.,though increasing an areal recording density of the magnetic recordingmedium 18 (expressed in Gigabits per square inch (Gb/in²)). Magneticstorage media 18 with smaller average grain diameters may allow anincrease in the areal recording density of the magnetic recording media.

High density perpendicular magnetic recording media may benefit from abalance of several magnetic properties in the magnetic recording layer,including high magnetic anisotropy for thermal stability; low switchingfield for writability of the recording layer by the magnetic recordinghead; sufficiently low lateral magnetic exchange coupling among themagnetic grains to maintain a small correlation length between magneticgrains or clusters; sufficiently high lateral magnetic exchange couplingamong the magnetic grains to maintain a narrow switching fielddistribution (SFD); and sufficient uniformity of magnetic propertiesamong the grains to maintain thermal stability and minimize the SFD.

As areal recording density continues to increase, magnetic grains with asmaller average diameter may be used to maintain at a similar value thenumber of magnetic grains in a recorded bit. However, magnetic stabilityof magnetic recording media becomes a greater concern as the averagegrain diameter decreases.

The magnetic grains maintain their magnetization orientation due tomagnetic anisotropy energy, which is proportional to the grain volume(K_(u)V, where K_(u) is magnetic anisotropy energy per unit volume and Vis volume). The magnetic anisotropy energy competes with thermal energyfluctuations, which would reorient the magnetization of the grainsrandomly. Thermal energy fluctuations depend on temperature of themagnetic recording layer (k_(B)T, where k_(B) is the Boltzmann constantand T is temperature). The ratio of magnetic anisotropy energy tothermal energy (K_(u)V/kT) is referred to as the energy barrier, whichis a measure of the magnetic stability of the grains and is proportionalto the volume of the respective grains. Thus, reducing grain size (grainvolume) increases areal density but reduces thermal stability, for thegrains having the same magnetic anisotropy energy per unit volume,K_(u). While K_(u) is the label for magnetic anisotropy energy per unitvolume, K_(u) will be termed magnetic anisotropy energy hereinafter forconciseness.

One method of overcoming the reduced thermal stability due to a decreasein average grain size is to increase an average anisotropy field, H_(k),of the magnetic grains. (H_(k)=2K_(u)/M_(s), where M_(s) is thesaturation magnetization of the material.) Magnetic grains having ahigher magnetic anisotropy field usually have higher magnetic anisotropyenergy, K_(u), and are thus more thermally stable than a similarly sizedgrain having a lower magnetic anisotropy field. However, increasing theaverage magnetic anisotropy field of the grains also may increase themagnetic field used to change the magnetic orientation of the grains,thus increasing the magnetic field used to record data.

Described herein are exchange-coupled composite (ECC) structures formagnetic recording layers, which may facilitate writing data to themagnetic recording layer while maintaining thermal stability (i.e., theenergy barrier) of the magnetic recording layer at or above anacceptable value. In some embodiments, the ECC structures describedherein both facilitate writing data to the magnetic recording layer andincrease thermal stability of the recording layer compared to some othermagnetic recording layers.

Some ECC structures have been proposed in which the magnetic recordinglayer is composed of a continuously graded material (e.g., a compositionof the magnetic recording layer changes substantially continuously andis not divided into separate sub-layers). In such continuously-gradedECC structures, it has further been proposed that the compositiongradient should be selected such that a magnetic anisotropy of themagnetic recording layer decreases proportional to a distance from thehighest anisotropy portion, squared (H_(k)∝1/x², where x is the distancefrom the highest anisotropy portion). In other words, it has beensuggested that the magnetic anisotropy of the magnetic recording layershould decrease more quickly in and proximate to the high anisotropyportion of the magnetic recording layer and more slowly as the distancefrom the high anisotropy portion increases. As illustrated in FIG. 2,this results in a concave shape to a plot of magnetic anisotropy versusposition in the magnetic recording layer. In examples in which such aH_(k) ∝ 1/x² magnetic anisotropy gradient has been proposed, the highestanisotropy portion of the magnetic recording layer is thermally stablewithout the contribution of the remaining, lower anisotropy portions ofthe recording layer.

Magnetic recording media 18 shown in FIG. 1 includes an ECC recordinglayer structure according to the present disclosure. A schematic blockdiagram of one embodiment of an ECC recording layer according to thepresent disclosure is illustrated in FIG. 3. Magnetic recording medium18 illustrated in FIG. 3 includes a substrate 32, a soft under layer(SUL) 34, a first interlayer 36, a second interlayer 38, a perpendicularrecording layer 40, and a protective overcoat 54.

Substrate 32 may include any material that is suitable to be used inmagnetic recording media, including, for example, Al, NiP plated Al,glass, or ceramic glass.

Although not shown in FIG. 2, in some embodiments, an additionalunderlayer may be present immediately on top of substrate 32. Theadditional underlayer may be amorphous and provides adhesion to thesubstrate and low surface roughness.

A soft underlayer (SUL) 34 is formed on substrate 32 (or the additionalunderlayer, if one is present). SUL 34 may be any soft magnetic materialwith sufficient saturation magnetization (M_(s)) and low magneticanisotropy field (H_(k)). For example, SUL 34 may be an amorphous softmagnetic material such as Ni; Co; Fe; an Fe-containing alloy such asNiFe (Permalloy), FeSiAl, or FeSiAlN; a Co-containing alloy such asCoZr, CoZrCr, or CoZrNb; or a CoFe-containing alloy such as CoFeZrNb,CoFe, FeCoB, or FeCoC.

First interlayer 36 and second interlayer 38 may be used to establish anHCP (hexagonal close packed) crystalline orientation that induces HCP(0002) growth of the first magnetic layer 42, with a magnetic easy axisperpendicular to the film plane.

A protective overcoat 54, such as, for example, diamond like carbon, maybe formed over perpendicular recording layer 40. In other examples,protective overcoat 54 may include, for example, an amorphous carbonlayer that further includes hydrogen or nitrogen. Although notillustrated in FIG. 3, in some examples, a lubricant layer may be formedon protective overcoat 54.

Perpendicular recording layer 40 may be formed on second interlayer 38,and may include a first magnetic layer 42, a first exchange break layer44, a second magnetic layer 46, a second exchange break layer 48, athird magnetic layer 50, and, optionally, a CGC layer 52. First magneticlayer 42 has a first magnetic anisotropy field, H_(k1), second magneticlayer 46 has a second magnetic anisotropy field, H_(k2), and thirdmagnetic layer 50 has a third magnetic anisotropy field, H_(k3). Themagnetic anisotropies of first magnetic layer 42, second magnetic layer46, and third magnetic layer 50 are each oriented in a directionsubstantially perpendicular to the plane of recording layer 40 (e.g.,the magnetic easy axes of first magnetic layer 42, second magnetic layer46, and third magnetic layer 50 may each be substantially perpendicularto the plane of recording layer 40). First exchange break layer 44 maybe used to adjust the vertical exchange coupling between first magneticlayer 42 and second magnetic layer 46, and second exchange break layer48 may be used to adjust vertical exchange coupling between secondmagnetic layer 46 and third magnetic layer 50. In some examples,magnetic recording layer 40 may include additional exchange break layersand magnetic layers (e.g., n magnetic layers and as many as n−1 exchangebreak layers).

Each of first magnetic layer 42, second magnetic layer 46, and thirdmagnetic layer 50 may be granular, and may include magnetic grainssubstantially separated from adjacent magnetic grains by non-magneticmaterial. In some embodiments, at least one of first magnetic layer 42,second magnetic layer 46, and third magnetic layer 50 may include a Coalloy, for example, Co in combination with at least one of Cr, Ni, Pt,Ta, B, Nb, O, Ti, Si, Mo, Cu, Ag, Ge, or Fe. In some embodiments, atleast one of first magnetic layer 42, second magnetic layer 46, andthird magnetic layer 50 may include, for example, an Fe—Pt alloy or aSm—Co alloy. In some embodiments, at least one of first magnetic layer42, second magnetic layer 46, and third magnetic layer 50 may includealternating thin layers of a Co alloy and a Pt alloy or a Co alloy and aPd alloy. In some embodiments, the non-magnetic material separating thegrains in at least one of first magnetic layer 42, second magnetic layer46, and third magnetic layer 50 may comprise an oxide, such as, forexample, SiO₂, TiO₂ CoO, Cr₂O₃, Ta₂O₅, which separate the magneticgrains. In other embodiments, the non-magnetic material separating thegrains in at least one of first magnetic layer 42, second magnetic layer46, and third magnetic layer 50 may comprise Cr, B, C, or anothernon-ferromagnetic element.

In some examples, at least one of first magnetic layer 42, secondmagnetic layer 46, and third magnetic layer 50 may comprise a Co—Ptalloy. One method of controlling a magnetic anisotropy field of thelayers 42, 46, 50 is controlling the Pt content of the respectivelayers. For example, a magnetic layer including a greater Pt content mayhave a higher magnetic anisotropy field than a magnetic layer includinga lower Pt content. In some examples, a high magnetic anisotropy fieldlayer may include greater than approximately 18 at. % Pt. In accordancewith some examples of the disclosure, the H_(k) gradient may be definedby the Pt content of first magnetic layer 42, second magnetic layer 46,and third magnetic layer 50. In other words, in some examples,Pt₁−Pt₂<Pt₂−Pt₃, where Pt₁ is the Pt content of first magnetic layer 42,Pt₂ is the Pt content of second magnetic layer 46, and Pt₃ is the Ptcontent of third magnetic layer 50. In one embodiment, Pt₁ is betweenapproximately 18 at. % and approximately 22 at. %, Pt₂ is betweenapproximately 14 at. % and approximately 18 at. %, and Pt₃ is less thanapproximately 14 at. %, and Pt₁−Pt₂<Pt₂−Pt₃.

First exchange break layer 44 and second exchange break layer 48 eachcomprise a material with relatively low saturation magnetization(M_(s)). For example, at least one of first exchange break layer 44 andsecond exchange break layer 48 may include a Co_(x)Ru_(1-x) alloy. Asanother example, at least one of first exchange break layer 44 andsecond exchange break layer 48 may include or consist essentially ofruthenium. As used herein, “consist essentially of” may indicate thatthe layer consists of the named material, but may include impuritiesdeposited with the named material, or other elements or materials thathave diffused into the layer from adjacent layers. In examples in whichfirst exchange break layer 44 or second exchange break layer 48comprises a Co_(x)Ru_(1-x) alloy, the break layer 44 or 48 may comprisea thickness of less than approximately 3 nm. In examples in which firstexchange break layer 44 or second exchange break layer 48 consistsessentially of Ru, the break layer 44 or 48 may be thinner, e.g., lessthan approximately 3 Å.

In addition to Ru or a Co_(x)Ru_(1-x) alloy, first exchange break layer44 and/or second exchange break layer 48 may optionally comprise anon-magnetic oxide, such as, for example, SiO₂, TiO₂, CoO₂, Cr₂O₃,Ta₂O₅. The non-magnetic oxide may serve to facilitate subsequentdeposition of a granular second magnetic layer 44 on first exchangebreak layer 44 or a granular third magnetic layer 50 on second exchangebreak layer 48. In some embodiments, first exchange break layer 44 andsecond exchange break layer 48 may comprise substantially similarcompositions, while in other embodiments, first exchange break layer 44and second exchange break layer 48 may comprise different compositions.

Magnetic recording layer 40 optionally may further include CGC layer 52.CGC layer 52 may comprise, for example, a CoCrPtB alloy. In someembodiments, the CoCrPtB alloy may be doped by a metal or rare earthelement, such as, for example, Ru, W, or Nb. In some embodiments, CGClayer 52 may include a small amount of an oxide, such as, for example,SiO_(x), TiO_(x), TaO_(x), WO_(x), NbO_(x), CrO_(x), CoO_(x). In otherembodiments, CGC layer 52 may not include an oxide (i.e., may be freefrom any oxide).

The particular compositions of first magnetic layer 42, second magneticlayer 46, and third magnetic layer 50 may be selected to provide apredetermined magnetic anisotropy field, H_(k), for each of therespective layers 42, 46, 50. In particular, the composition of firstmagnetic layer 42 may be selected to provide a first magnetic anisotropyfield, H_(k1), the composition of second magnetic layer 46 may beselected to provide a second magnetic anisotropy field, H_(k2), and acomposition of third magnetic layer 50 may be selected to provide athird magnetic anisotropy field, H_(k3). In some embodiments, themagnetic anisotropy field of the hardest magnetic layer, which may befirst magnetic layer 42 in some implementations, may be limited to amagnetic anisotropy field of approximately 30 kOe (e.g., when formed ofa Co alloy). Because of this, the hardest magnetic layer may not besufficiently stable when an average grain size of magnetic recordinglayer 40 is sufficiently small. In order to overcome this, an averageanisotropy of first magnetic layer 42, second magnetic layer 46, andthird magnetic layer 50 may be relatively high such that at least two ofthe three magnetic layers 42, 46, 50 contribute to thermal stability ofthe magnetic orientation of magnetic recording layer 40.

One way to accomplish a relatively high average magnetic anisotropyfield for first magnetic layer 42, second magnetic layer 46, and thirdmagnetic layer 50, while still obtaining benefits provided by an ECCstructure, is to select the compositions of the first, second, and thirdmagnetic layers 42, 46, 50 such that a difference between H_(k1) andH_(k2) (i.e., H_(k1)−H_(k2)) is less than a difference between H_(k2)and H_(k3) (i.e., H_(k2)−H_(k3)). In other words, the magneticanisotropy of the individual layers 42, 46, 50 in magnetic recordinglayer 40 decreases more slowly, or may even increase, proximate to firstmagnetic layer 42, and decreases more rapidly as distance from firstmagnetic layer 42 increases. Such a distribution of magnetic anisotropyfields in magnetic recording layer 40 may be referred to as a convexmagnetic anisotropy field distribution. A convex magnetic anisotropyfield distribution may provide thermal stability of the magneticorientation of magnetic recording layer 40 and writability of therecording layer 40. In some examples, a convex magnetic anisotropydistribution may result in a greater proportion of magnetic recordinglayer 40 being formed of a material with a relatively high magneticanisotropy field.

The particular values of H_(k1), H_(k2), and H_(k3) may depend on, forexample, a recording head used to write data to magnetic recording layer40, a size of the individual grains in the respective layers 42, 46, 50,the respective magnetic anisotropy field of the other two layers, athickness of the respective layer, a saturation magnetization of therespective layer, or the like. In some embodiments, the range of H_(k)values for the respective layers 42, 46, 50 may be affected by thecontribution of the K_(u)V magnetic anisotropy energies of each of thelayers 42, 46, 50. For example, a first magnetic layer 42 with a lowervalue of K_(u)V is easier to write to than a first magnetic layer 42with a higher value of K_(u)V (i.e., it allows a lower applied magneticfield to switch magnetic orientation of the grains in a layer 42 with alower value of K_(u)V). Thus, a first magnetic layer 42 having a lowervalue of K_(u)V may allow use of a second magnetic layer 46 having alower H_(k2) value and a third magnetic layer 50 having a lower H_(k3)value to drive the ECC-assisted writing process. However, the lowervalue of K_(u)V may use a greater magnetic anisotropy energycontribution (K_(u)V) from second magnetic layer 46 and third magneticlayer 50 in order to maintain thermal stability of perpendicularrecording layer 40, as a whole. For a layer, e.g., second magnetic layer46, comprising a given H_(k) value, the K_(u)V anisotropy energycontribution may be affected by changing the saturation magnetization,M_(s), of the material, as K_(u)V=2H_(k)V/M_(s). Additionally oralternatively, the effective volume, V, can be changed by changing thelateral magnetic exchange among grains within the magnetic layer, whichcan change the effective magnetic cluster size (a cluster of grains thatchange magnetic orientation under substantially similar conditions).

The ranges of values which H_(k1), H_(k2), and H_(k3) may take may bedefined individually for simplicity, but may be better understood whendefined in combination with each other, as the differences betweenH_(k1) and H_(k2) and H_(k2) and H_(k3) are one way of defining thepredetermined magnetic recording layer structure. Considered alone,without reference to the H_(k) values of the other layers, H_(k1) may bebetween approximately 16 kOe and approximately 24 kOe in someembodiments. In other embodiments, H_(k1) may be greater thanapproximately 24 kOe or less than 16 kOe. Some examples of values forH_(k1) include approximately 20 kOe or approximately 24 kOe.

In some embodiments, H_(k2) may be between approximately 12 kOe andapproximately 24 kOe, while in other embodiments, H_(k2) may be greaterthan 24 kOe or less than 12 kOe. Some examples of values for H_(k2)include between approximately 12 kOe and approximately 15 kOe,approximately 16 kOe, approximately 19 kOe, or approximately 24 kOe.

In some embodiments, H_(k3) may be less than approximately 15 kOe, whilein other embodiments, H_(k3) may be greater than 15 kOe. Some examplesof values for H_(k3) include between approximately 3 kOe andapproximately 9 kOe, approximately 9 kOe, approximately 6 kOe, orapproximately 1 kOe.

Considered together, in some embodiments, H_(k1) may be betweenapproximately 16 kOe and approximately 24 kOe, H_(k2) may be betweenapproximately 12 kOe and approximately 24 kOe, and H_(k3) may be lessthan H_(k2), such that the values of H_(k1), H_(k2), and H_(k3) satisfythe relationship H_(k1)−H_(k2)<H_(k2)−H_(k3). In some embodiments,H_(k1) is between approximately 20 kOe and approximately 22 kOe, H_(k2)is between approximately 17 kOe and approximately 20 kOe, and H_(k3) isbetween approximately 9 kOe and approximately 14 kOe. In anotherembodiment, Pt concentration in layer 1 is approximately 18-22 at %, Ptconcentration in layer 2 is approximately 14-18 at %, and Ptconcentration in layer 3 is less than about 14 at %, H_(k2) isapproximately 17-20 kOe, and H_(k3) is approximately 9-14 kOe.

In some embodiments, the relationship between H_(k1), H_(k2), and H_(k3)may be further defined by a ratio between H_(k2) and H_(k1) and/or aratio between H_(k3) and H_(k2). For example, the ratio H_(k2)/H_(k1)may be greater than the ratio H_(k3)/H_(k2). In some embodiments,H_(k2)/H_(k1) may be greater than approximately 0.6 and H_(k3)/H_(k2)may be less than approximately 0.6. In some embodiments, H_(k2)/H_(k1)may be greater than approximately 0.7 and H_(k3)/H_(k2) may be less thanapproximately 0.7. In some embodiments, H_(k2)/H_(k1) may be greaterthan approximately 0.9 and H_(k3)/H_(k2) may be less than approximately0.9. In some embodiments, H_(k2)H_(k1) may be greater than approximately1.0 and H_(k3)/H_(k2) may be less than approximately 1.0. In oneembodiment, H_(k2)/H_(k1) may be approximately 1.2.

In some embodiments, regardless of the value of H_(k2)/H_(k1),H_(k3)/H_(k2) may be less than approximately 0.6. In some embodiments,H_(k3)/H_(k2) may be less than approximately 0.1.

The saturation magnetizations of first magnetic layer 42, secondmagnetic layer 46, and third magnetic layer 50 may be the same or may bedifferent. In some embodiments, the saturation magnetization, M_(s), ofeach of first magnetic layer 42, second magnetic layer 46, and thirdmagnetic layer 50 may be between approximately 350 emu/cm³ andapproximately 700 emu/cm³. In some examples, the saturationmagnetization of at least one of first magnetic layer 42, secondmagnetic layer 46, and third magnetic layer 50 may be betweenapproximately 450 emu/cm³ and approximately 700 emu/cm³. For example,the saturation magnetization of at least one of first magnetic layer 42,second magnetic layer 46, and third magnetic layer 50 may beapproximately 550 emu/cm³.

A thickness of first magnetic layer 42 may be between approximately 5 nmand approximately 10 nm. A thickness of second magnetic layer 46 may bebetween approximately 3 nm and approximately 7 nm, and a thickness ofthird magnetic layer 50 may be less than approximately 10 nm. Asdescribed above, a thickness of each of the respective magnetic layers42, 46, 50, may have an effect on the selection of the H_(k) valueand/or the M_(s) value for the respective layers 42, 46, 50. In oneembodiment, the thickness of second magnetic layer 46 may be less thanapproximately 4 nm and H_(k1)/H_(k2) is greater than approximately 0.8and H_(k2)/H_(k3) is less than approximately 0.8.

FIGS. 4A-4E are diagrams illustrating examples of magnetic anisotropyfield configurations for first magnetic layer 42, second magnetic layer46, and third magnetic layer 50. FIGS. 4A-4E illustrate examples ofconfigurations of magnetic recording layer 40 in which the compositionsof first magnetic layer 42, second magnetic layer 46, and third magneticlayer 50 are selected such that the difference H_(k1)−H_(k2) is lessthan the difference H_(k2)−H_(k3). As described above, the relationshipbetween H_(k1), H_(k2), and H_(k3) may be further defined by a firstratio H_(k2)/H_(k1) and/or a second ratio H_(k3)/H_(k2).

For example, FIG. 4A illustrates a magnetic recording layer 40 in whichH_(k1)−H_(k2) is less than H_(k2)−H_(k3). Additionally, H_(k2)/H_(k1)may be greater than approximately 0.6, and in some embodiments, may begreater than approximately 0.9. The ratio H_(k3)/H_(k2) of theconfiguration of magnetic recording layer 40 illustrated in FIG. 4A maybe less than approximately 0.6, and may be less than 0.1. For example,H_(k1) may be between approximately 16 kOe and approximately 24 kOe,H_(k2) may be between approximately 12 kOe and approximately 24 kOe, andH_(k3) may be less than approximately 15 kOe. In one embodiment, H_(k1)is approximately 20 kOe, H_(k2) is approximately 16 kOe, and H_(k3) isapproximately 9 kOe. In another embodiment, H_(k1) is approximately 20kOe, H_(k2) is approximately 19 kOe, and H_(k3) is approximately 6 kOe.In a further embodiment, H_(k1) is approximately 24 kOe, H_(k2) isapproximately 16 kOe, and H_(k3) is approximately 1 kOe.

As another example, FIG. 4B illustrates a magnetic recording layer 40 inwhich H_(k1)−H_(k2) is less than H_(k2)−H_(k3). Additionally,H_(k1)−H_(k2) is less than zero, and H_(k2)/H_(k1) is greater thanapproximately 1.0, such as, for example, approximately 1.2. In theembodiment illustrated in FIG. 4B, the ratio H_(k3)/H_(k2) may be lessthan approximately 0.6 and, in some embodiments, may be less thanapproximately 0.1. In one embodiment, H_(k1) is approximately 20 kOe,H_(k2) is approximately 24 kOe, and H_(k3) is approximately 1 kOe.

FIGS. 4C-4E illustrate embodiments in which magnetic recording layer 40includes a CGC layer 52 formed on third magnetic layer 50. Inembodiments in which CGC layer 52 is formed directly on third magneticlayer 50, CGC layer 52 and third magnetic layer 50 may act as a singlecomposite layer for purposes of the ECC effect of third magnetic layer50 and CGC layer 52 on second magnetic layer 46 and first magnetic layer42. In other words, a thickness-weighted average magnetic anisotropyfield, H_(k34), may be approximated by a thickness-weighted average ofH_(k3) and a magnetic anisotropy field of CGC layer 52, H_(k4). Thecomposite layer (third magnetic layer 50 and CGC layer 52) may beconsidered together for contribution of magnetic anisotropy energyK_(u)V, and the calculation of K_(u)V for the composite layer may bemade based on the combined thickness and magnetic moment of thirdmagnetic layer 50 and CGC layer 52. The composite layer comprising thirdmagnetic layer 50 and CGC layer 52 may exert an ECC effect on secondmagnetic layer 46 and first magnetic layer 42 substantially similar to asingle layer comprising a magnetic anisotropy field H_(k34). Lateralexchange coupling among grains within CGC layer 52 may decrease theapplied magnetic field used to switch magnetic orientation of grainswithin CGC layer 52 compared to a layer with an equal H_(k) but lowerlateral exchange coupling. Thus, in some embodiments, the effectiveH_(k34) may be lower than the thickness-weighted average of H_(k3) andH_(k4). Accordingly, in some embodiments, only H_(k3) and not H_(k4) maybe considered when defining the convex magnetic anisotropy grading.

In some embodiments, as illustrated in FIGS. 4C and 4D, CGC layer 52 maycomprise a magnetic anisotropy field, H_(k4), that is less than orsubstantially equal to H_(k3). In some embodiments, as illustrated inFIG. 4C, a difference between the magnetic anisotropy fields of CGClayer 52 and third magnetic layer 50, H_(k4)−H_(k3), may be greater thanthe difference H_(k3)−H_(k2). In other words, the convex magneticanisotropy field gradient may extend into CGC layer 52.

In other embodiments, as illustrated by FIG. 4D, H_(k4)−H_(k3) may notbe greater than the difference H_(k3)−H_(k2). In such an embodiment, theconvex magnetic anisotropy field gradient may not extend into CGC layer52, but may extend substantially through first magnetic layer 42, secondmagnetic layer 46, and third magnetic layer 50.

In other embodiments, as illustrated in FIG. 4E, CGC layer 52 maycomprise a magnetic anisotropy field, H_(k4), which is greater thanH_(k3). Similar to an embodiment in which H_(k4)−H_(k3) is not greaterthan the difference H_(k3)−H_(k2), when H_(k4) is greater than H_(k3),the convex magnetic anisotropy field gradient may not extend into CGClayer 52, but may extend substantially through first magnetic layer 42,second magnetic layer 46, and third magnetic layer 50.

Although the above embodiments have been directed to a magneticrecording layer including three magnetic layers and, optionally, a CGClayer, in some embodiments a magnetic recording layer may include morethan three magnetic layers. In general, the concept of a magneticrecording layer including a convex magnetic anisotropy gradient may beextended to any number of magnetic layers. For example, as shown in FIG.5A, a magnetic recording layer 60 may include (2n−1) layers, including nmagnetic layers alternating with n−1 exchange break layers, where n isan integer greater than or equal to 3. Additionally and optionally,magnetic recording layer 61 may include a CGC layer 71 formed onmagnetic layer n, as shown in FIG. 5B. In particular, FIG. 5Aillustrates a first magnetic layer 62, which may be a granular magneticlayer with a composition that results in a relatively high magneticanisotropy field. The magnetic anisotropy field of first magnetic layer62 is oriented in a direction substantially perpendicular to the planeof recording layer 60 (e.g., the magnetic easy axes of grains in firstmagnetic layer 62 may be substantially perpendicular to the plane ofrecording layer 60). First magnetic layer 62 may comprise a Co alloy,for example, Co in combination with at least one of Cr, Ni, Pt, Ta, B,Nb, 0, Ti, Si, Mo, Cu, Ag, Ge, or Fe. In some embodiments, firstmagnetic layer 62 may include, for example, an Fe—Pt alloy or a Sm—Coalloy. In some embodiments, first magnetic layer 62 may includealternating thin layers of a Co alloy and a Pt alloy or a Pd alloy. Insome embodiments, the non-magnetic material separating the grains infirst magnetic layer 62 may comprise an oxide, such as, for example,SiO₂, TiO₂ CoO, Cr₂O₃, Ta₂O₅, which separate the magnetic grains. Inother embodiments, the non-magnetic material separating the grains infirst magnetic layer 62 may comprise Cr, B, C, or othernon-ferromagnetic elements.

First exchange break layer 64 is formed on first magnetic layer 62.First exchange break layer 64 may include a Co_(x)Ru_(1-x) alloy. Asanother example, first exchange break layer 64 may include or consistessentially of ruthenium. In examples in which first exchange breaklayer 64 comprises a Co_(x)Ru_(1-x) alloy, the break layer 64 maycomprise a thickness of less than approximately 3 nm. In examples inwhich first exchange break layer 64 consists essentially of Ru, thebreak layer 64 may be thinner, e.g., less than approximately 3 Å.

Second magnetic layer 66 is formed on first exchange break layer 64, andmay be a granular magnetic layer with a composition that results in amagnetic anisotropy field that is relatively high. As described above,second magnetic layer 66 may have a magnetic anisotropy that is lessthan, substantially equal to, or greater than the magnetic anisotropy offirst magnetic layer 62. The magnetic anisotropy of second magneticlayer 66 is oriented in a direction substantially perpendicular to theplane of recording layer 60 (e.g., the easy axes of grains in secondmagnetic layer 66 may be substantially perpendicular to the plane ofrecording layer 60). Second magnetic layer 66 may comprise a Co alloy,such as Co in combination with at least one of Cr, Ni, Pt, Ta, B, Nb, O,Ti, Si, Mo, Cu, Ag, Ge, or Fe. In some embodiments, second magneticlayer 66 may include, for example, an Fe—Pt alloy or a Sm—Co alloy. Insome embodiments, second magnetic layer 66 may include alternating thinlayers of a Co alloy and a Pt alloy or a Pd alloy. In some embodiments,the non-magnetic material separating the grains in second magnetic layer66 may comprise an oxide, such as, for example, SiO₂, TiO₂ CoO, Cr₂O₃,Ta₂O₅, which separate the magnetic grains. In other embodiments, thenon-magnetic magnetic material separating the grains in second magneticlayer 66 may comprise Cr, B, C, or another non-ferromagnetic element.

Magnetic recording layer 60 may include an arbitrary number of magneticlayers and exchange break layers in an alternating pattern. Eachsubsequent magnetic layer may have composition selected such thatmagnetic recording layer 60 includes a convex magnetic anisotropy fieldgradient among its plurality of magnetic layers. In other words, thecompositions of the respective magnetic layer may be selected such thatH_(k(n-2))−H_(k (n-1)) is less than H_(k(n-1))−H_(K(n)), where H_(ki) isthe magnetic anisotropy field of layer i. For example, the compositionsof first magnetic layer 62, second magnetic layer 66, and a thirdmagnetic layer (not shown) may be selected such that H_(k1)−H_(k2) isless than H_(k2)−H_(k3). Exchange break layer n−1 68 is formed onmagnetic layer n−1 (not shown). Exchange break layer n−1 68 may compriseruthenium or a ruthenium alloy, and may have a similar composition tofirst exchange break layer 64 or a different composition than firstexchange break layer 64. In some embodiments, exchange break layer n−168 may consist essentially of or consist of ruthenium, while in otherembodiments, exchange break layer n−1 68 may comprise a ruthenium alloy,e.g., Co_(x)Ru_(1-x). In addition to Ru or a Co_(x)Ru_(1-x) alloy,exchange break layer n−1 68 may optionally include a non-magnetic oxide,such as, for example, SiO₂, TiO₂ CoO, Cr₂O₃, or Ta₂O₅.

Magnetic layer n 70 is formed on exchange break layer n−1 68, and insome embodiments may be a granular magnetic layer with magneticanisotropy that is relatively low, e.g., lower than the magneticanisotropy of any other of the magnetic layers in recording layer 60.Magnetic layer n has a magnetic anisotropy field oriented in a directionsubstantially perpendicular to the plane of recording layer 60. Magneticlayer n 70 may include, for example, a Co alloy, an Fe—Pt alloy, or aSm—Co alloy, and may or may not include a non-magnetic oxide, such as,for example, SiO₂, TiO₂ CoO, Cr₂O₃, Ta₂O₅, as described above. Thecomposition of magnetic layer n 70 may be different than the compositionof first magnetic layer 62 and/or second magnetic layer 66, such thatmagnetic layer n 70 has a magnetic anisotropy field that, along with themagnetic anisotropy fields of the other magnetic layers in magneticrecording layer 60, results in a convex magnetic field gradient. Forexample, magnetic layer n 70 may include similar components as firstmagnetic layer 62 and/or second magnetic layer 66, but in differentproportions.

In some embodiments, CGC layer 71 (shown in FIG. 5B) may be similar toCGC layer 52 described above with reference to FIG. 3.

A method of forming a perpendicular magnetic recording layer isillustrated in FIG. 6. The method may forming a first magnetic layerhaving a magnetic anisotropy field, H_(k1) (72), forming a firstexchange break layer on the first magnetic layer (74), and forming asecond magnetic layer on the first exchange break layer (76). The secondmagnetic layer has a second magnetic anisotropy field, H_(k2). In someembodiments, the method further includes forming a second exchange breaklayer on the second magnetic layer (78) and forming a third magneticlayer on the second exchange break layer (80). The third magnetic layerhas a third magnetic anisotropy field, H_(k3). In some embodiments,H_(k1)−H_(k2) is less than H_(k2)−H_(k3).

Although magnetic recording layers described herein have included breaklayers alternating with magnetic layers, in some embodiments, a magneticrecording layer may not include a break layer between each pair ofadjacent magnetic layers. For example, a magnetic recording layer mayinclude a second magnetic layer 46 and a third magnetic layer 50 (FIG.3) formed immediately adjacent each other, without an intervening secondbreak layer 48. This concept may be extended to other pairs of magneticlayers, such as first magnetic layer 42 and second magnetic layer 46.Additionally, in embodiments including more than three magnetic layers(e.g., embodiments such as those described with reference to FIG. 5),magnetic recording layer 60 may include as many as 2n−1 layers,including n magnetic layers and as many as n−1 break layers. In suchembodiments, some adjacent magnetic layer pairs may include interveningbreak layers, and other adjacent magnetic layer pairs may not includeintervening break layers.

Although the foregoing disclosure has been primarily directed to anapparatus that includes a magnetic recording medium, the magnetic layerstructure described herein may also be utilized in other applications.For example, the magnetic layer structure described herein may beutilized in a magnetic sensor or magnetoresistive random access memory(MRAM).

EXAMPLES

The following examples are illustrative of embodiments of thedisclosure, but do not limit the scope of the disclosure. The exampleswere based on theoretical calculations using idealized magnetic layers.The magnetic layers each had the same values of M_(s) and H_(ex). Themagnetic recording layers in the examples did not include a CGC layer.In the following examples, parameters are defined as following. Equation1 defines an effective magnetic thickness of a layer i, Δ_(i):

$\begin{matrix}{\Delta_{i} = \frac{M_{si}\delta_{i}}{M_{s\; 1}\delta_{1\;}}} & {{Equation}\mspace{14mu} 1}\end{matrix}$

where M_(s), is a saturation magnetization of layer i, δ_(i) is athickness of layer i, M_(s1) is a saturation magnetization of layer 1(i.e., a first magnetic layer), and δ₁ is a thickness of layer 1.

Equation 2 defines an effective anisotropy of a layer i, κ_(i):

$\begin{matrix}{\kappa_{i} = {\frac{M_{si}H_{Ai}\delta_{i}}{M_{s\; 1}H_{A\; 1}\delta_{1}} = {\Delta_{i}\frac{H_{Ai}}{H_{A\; 1}}}}} & {{Equation}\mspace{14mu} 2}\end{matrix}$

where M_(si) is a saturation magnetization of layer i, H_(Ai) is amagnetic coercivity of layer i, δ_(i) is a thickness of layer i, M_(s1)is a saturation magnetization of layer 1, H_(A1) is a magneticcoercivity of layer 1, and δ₁ is a thickness of layer 1.

Equation 3 defines an effective coupling between a layer i and a layerj, χ_(ij):

$\begin{matrix}{\chi_{ij} = \frac{2J_{ij}}{K_{1}\delta_{1}}} & {{Equation}\mspace{14mu} 3}\end{matrix}$

where J_(ij) is a quantum mechanical coupling between layer i and layerj, K₁ is a magnetic anisotropy energy of layer 1, and δ₁ is a thicknessof layer 1.

For the following Examples, certain parameters were held fixed. Forexample, Δ₂=Δ₃=0.5 Δ₁. In other words, the effective thicknesses oflayers 2 and 3 were set to be equal, and each one-half the effectivethickness of layer 1.

In evaluating Examples 1-3 below, comparison was made to a respectivecoherently switching three-layer magnetic recording layer, in which thethree magnetic layers had magnetic anisotropies of H_(A1),H_(A2)=0.75H_(A1), and H_(A3)=0.5H_(A1). Such a magnetic anisotropydistribution resulted in an average magnetic anisotropy <H_(A)> of0.8125H_(A1). In making the Examples, then, <H_(A)> was kept constant,and a κ₂ value was selected, which set the κ₃ value. χ₁₂ and χ₂₃ werefree parameters.

Example 1

FIGS. 6A and 6B illustrate an example in which the magnetic anisotropyvalue, H_(A1), of magnetic layer 1 was 20 kOe, the magnetic anisotropyvalue, H_(A2), of magnetic layer 2 was 16 kOe, and the magneticanisotropy value, H_(A3), of magnetic layer 3 was 9 kOe. Such magneticanisotropy distribution is a convex magnetic anisotropy gradientaccording to the disclosure. H_(A1)−H_(A2) is 4 kOe, which is less thanH_(A2)−H_(A3), which is 7 kOe. Further, H_(A2)/H_(A1) is 0.8, which isgreater than H_(A3)/H_(A2) (0.5625). In Example 1, Δ₂=Δ₃=0.5, κ₂=0.4,and κ₃=0.225.

Magnetic orientation switching performance of Example 1 was comparedwith a reference three-layer magnetic recording layer that switchedcoherently, e.g., in which the three magnetic layers were coupled andacted as a single magnetic layer with an effective anisotropy calculatedas an effective thickness-weighted average of the anisotropies of therespective layers. The first magnetic layer had an anisotropy ofH_(A1)=20 kOe and a relative effective thickness of 1, the secondmagnetic layer had an anisotropy of H_(A2)=0.8H_(A1)=16 kOe and arelative effective thickness of 0.5, and the third magnetic layer had ananisotropy of H_(A3)=0.45H_(A1)=9 kOe and a relative effective thicknessof 0.5. Such a magnetic anisotropy distribution resulted in an effectivethickness-weighted average magnetic anisotropy <H_(A)> of0.8125H_(A1)=16.25 kOe, and an energy barrier change ΔE/ΔE₁ of 1.625.The energy barrier change indicates the effect the second and thirdmagnetic layers have on thermal stability of the magnetic recordinglayer compared to a magnetic recording layer including only the firstmagnetic layer.

In comparing magnetic orientation switching performance of Example 1with the reference coherently-switching magnetic recording layer, aminimum normalized H_(sw) value (an effective coercivity of the magneticrecording layer; equal to the applied magnetic field at which theorientation of the magnetic recording layer switched, normalized by thecoercivity of the first magnetic layer) was found at an energy barriersubstantially equal to the energy barrier of the reference magneticrecording layer (1.625). With reference to FIGS. 6A and 6B, approximatecoordinates of circle 82 are χ₁₂=0.45 and χ₂₃=0.45. Turning to FIG. 6A,the normalized H_(sw) value at χ₁₂=0.45 and χ₂₃=0.45 is approximately0.73, as illustrated by circle 84. Comparing this to the normalizedH_(sw) value of the reference film, 0.8125, the magnetic anisotropygradient in Example 1 provides a reduction in normalized H_(sw) ofapproximately 11%. In other words, a magnetic recording layer comprisingthree magnetic layers selected to provide a convex magnetic anisotropygradient may switch more easily than and have comparable thermalstability to a magnetic recording layer comprising three magnetic layersselected to provide a linear magnetic anisotropy gradient.

Example 2

FIGS. 7A and 7B illustrate an example in which the magnetic anisotropyvalue, H_(A1), of magnetic layer 1 was 20 kOe, the magnetic anisotropyvalue, H_(A2), of magnetic layer 2 was 19 kOe, and the magneticanisotropy value, H_(A3), of magnetic layer 3 was 6 kOe. Such magneticanisotropy distribution is a convex magnetic anisotropy gradientaccording to the disclosure. H_(A1)−H_(A2) is 1 kOe, which is less thanH_(A2)−H_(A3), which is 13 kOe. Further, H_(A2)/H_(A1) is 0.95, which isgreater than H_(A3)/H_(A2) (0.3158). In Example 1, Δ₂=Δ₃=0.5, κ₂=0.475,and κ3=0.15.

Magnetic orientation switching performance of Example 2 was comparedwith a reference three-layer magnetic recording layer that switchedcoherently, e.g., in which the three magnetic layers were coupled andacted as a single magnetic layer with an effective anisotropy calculatedas an effective thickness-weighted average of the anisotropies of therespective layers. The first magnetic layer had an anisotropy ofH_(A1)=20 kOe and a relative effective thickness of 1, the secondmagnetic layer had an anisotropy of H_(A2)=0.95H_(A1)=19 kOe and arelative effective thickness of 0.5, and the third magnetic layer had ananisotropy of H_(A3)=0.3H_(A1)=6 kOe and a relative effective thicknessof 0.5. Such a magnetic anisotropy distribution resulted in an averagemagnetic anisotropy <H_(A)> of 0.8125H_(A1)=16.25 kOe, and an energybarrier change ΔE/ΔE₁ of 1.625. The energy barrier change indicates theeffect the second and third magnetic layers have on thermal stability ofthe magnetic recording layer compared to a magnetic recording layerincluding only the first magnetic layer.

In comparing magnetic orientation switching performance of Example 2with the reference coherently-switching magnetic recording layer, aminimum normalized H_(sw) value was found at an energy barriersubstantially equal to the energy barrier of the reference magneticrecording layer (1.625). With reference to FIGS. 7A and 7B, approximatecoordinates of circle 86 are χ₁₂=0.45 and χ₂₃=0.45. Turning to FIG. 7A,the normalized H_(sw) value at χ₁₂=0.45 and χ₂₃=0.45 is approximately0.68, as illustrated by circle 88. Comparing this to the normalizedH_(sw) value of the reference film, 0.8125, the magnetic anisotropygradient in Example 1 provides a reduction in normalized H_(sw) ofapproximately 20%. Again, a magnetic recording layer comprising threemagnetic layers selected to provide a convex magnetic anisotropygradient may switch more easily than and have comparable thermalstability to a magnetic recording layer comprising three magnetic layersselected to provide a linear magnetic anisotropy gradient.

Example 3

FIGS. 8A and 8B illustrate an example in which the magnetic anisotropyvalue, H_(A1), of magnetic layer 1 was 20 kOe, the magnetic anisotropyvalue, H_(A2), of magnetic layer 2 was 24 kOe, and the magneticanisotropy value, H_(A3), of magnetic layer 3 was 1 kOe. Such magneticanisotropy distribution is a convex magnetic anisotropy gradientaccording to the disclosure. H_(A1)−H_(A2) is −4 kOe, which is less thanH_(A2)−H_(A3), which is 23 kOe. Further, H_(A2)/H_(A1) is 1.2, which isgreater than H_(A3)/H_(A2) (0.0417). In Example 1, Δ₂=Δ₃=0.5, κ₂=0.6,and κ₃=0.025.

Magnetic orientation switching performance of Example 3 was comparedwith a reference three-layer magnetic recording layer that switchedcoherently, e.g., in which the three magnetic layers were coupled andacted as a single magnetic layer with an effective anisotropy calculatedas an effective thickness-weighted average of the anisotropies of therespective layers. The first magnetic layer had an anisotropy ofH_(A1)=20 kOe and a relative effective thickness of 1, the secondmagnetic layer had an anisotropy of H_(A2)=1.2H_(A1)=24 kOe and arelative effective thickness of 0.5, and the third magnetic layer had ananisotropy of H_(A3)=0.05H_(A1)=1 kOe and a relative effective thicknessof 0.5. Such a magnetic anisotropy distribution resulted in an averagemagnetic anisotropy <H_(A)> of 0.8125H_(A1)=16.25 kOe, and an energybarrier change ΔE/ΔE₁ of 1.625. The energy barrier change indicates theeffect the second and third magnetic layers have on thermal stability ofthe magnetic recording layer compared to a magnetic recording layerincluding only the first magnetic layer.

In comparing magnetic orientation switching performance of Example 1with the reference coherently-switching magnetic recording layer, aminimum normalized H_(sw) value (an effective coercivity of the magneticrecording layer; equal to the applied magnetic field at which theorientation of the magnetic recording layer switched, normalized by theanisotropy of the first magnetic layer) was found at an energy barriersubstantially equal to the energy barrier of the reference magneticrecording layer (1.625). With reference to FIGS. 8A and 8B, approximatecoordinates of circle 90 are χ₁₂=0.45 and χ₂₃=0.45. Turning to FIG. 8A,the normalized H_(sw) value at χ₁₂=0.45 and χ₂₃=0.45 is approximately0.55, as illustrated by circle 92. Comparing this to the normalizedH_(sw) value of the reference film, 0.8125, the magnetic anisotropygradient in Example 1 provides a reduction in normalized H_(sw) ofapproximately 48%. This demonstrates that a magnetic recording layercomprising three magnetic layers selected to provide a convex magneticanisotropy gradient may switch more easily than and have comparablethermal stability to a magnetic recording layer comprising threemagnetic layers selected to provide a linear magnetic anisotropygradient.

Example 4

FIGS. 9A and 9B illustrate an example in which the magnetic anisotropyvalue, H_(A1), of magnetic layer 1 was 24 kOe, the magnetic anisotropyvalue, H_(A2), of magnetic layer 2 was 16 kOe, and the magneticanisotropy value, H_(A3), of magnetic layer 3 was 1 kOe. Such magneticanisotropy distribution is a convex magnetic anisotropy gradientaccording to the disclosure. H_(A1)−H_(A2) is 4 kOe, which is less thanH_(A2)−H_(A3), which is 15 kOe. Further, H_(A2)/H_(A1) is 0.667, whichis greater than H_(A3)/H_(A2) (0.0625). In Example 1, Δ₂=Δ₃=0.5, κ₂=⅓,and κ₃= 1/48.

Magnetic orientation switching performance of Example 4 was comparedwith a reference three-layer magnetic recording layer that switchedcoherently, e.g., in which the three magnetic layers were coupled andacted as a single magnetic layer with an effective anisotropy calculatedas an effective thickness-weighted average of the anisotropies of therespective layers. The first magnetic layer had an anisotropy ofH_(A1)=24 kOe and a relative effective thickness of 1, the secondmagnetic layer had an anisotropy of H_(A2)=(⅔)H_(A1)=16 kOe and arelative effective thickness of 0.5, and the third magnetic layer had ananisotropy of H_(A3)=( 1/24)H_(A1)=1 kOe and a relative effectivethickness of 0.5. Such a magnetic anisotropy distribution resulted in anaverage magnetic anisotropy <H_(A)> of 0.677H_(A1)=16.25 kOe, and anenergy barrier change ΔE/ΔE₁ of 1.354. The energy barrier changeindicates the effect the second and third magnetic layers have onthermal stability of the magnetic recording layer compared to a magneticrecording layer including only the first magnetic layer.

In comparing magnetic orientation switching performance of Example 4with the reference coherently-switching magnetic recording layer, aminimum normalized H_(sw) value was found at an energy barriersubstantially equal to the energy barrier of the reference magneticrecording layer (1.354). With reference to FIGS. 9A and 9B, approximatecoordinates of circle 94 are χ₁₂=0.35 and χ₂₃=0.4. Turning to FIG. 9A,the normalized H_(sw) value at χ₁₂=0.35 and χ₂₃=0.4 is approximately0.42, as illustrated by circle 96. Comparing this to the normalizedH_(sw) value of the reference film, 0.677, the magnetic anisotropygradient in Example 4 provides a reduction in normalized H_(sw) ofapproximately 61%. This demonstrates that a magnetic recording layercomprising three magnetic layers selected to provide a convex magneticanisotropy gradient may switch more easily than and have comparablethermal stability to a magnetic recording layer comprising threemagnetic layers selected to provide a linear magnetic anisotropygradient.

Various embodiments of the disclosure have been described. Theimplementations described above and other implementations are within thescope of the following claims.

1. An apparatus comprising: a first magnetic layer having a firstmagnetic anisotropy field, H_(k1); a first exchange break layer formedon the first magnetic layer; a second magnetic layer formed on the firstexchange break layer, wherein the second magnetic layer has a secondmagnetic anisotropy field, H_(k2); a second exchange break layer formedon the second magnetic layer; and a third magnetic layer formed on thesecond exchange break layer, wherein the third magnetic layer has athird magnetic anisotropy field, H_(k3), and wherein H_(k1)−H_(k2) isless than H_(k2)−H_(k3).
 2. The apparatus of claim 1, wherein a firstratio H_(k2)/H_(k1) is greater than a second ratio H_(k3)/H_(k2).
 3. Theapparatus of claim 2, wherein a first ratio is greater thanapproximately 0.6.
 4. The apparatus of claim 2, wherein the first ratiois greater than approximately 0.9.
 5. The apparatus of claim 2, whereinthe first ratio is greater than approximately 1.0.
 6. The apparatus ofclaim 1, wherein the first magnetic layer comprises a Pt content, Pt₁,content between approximately 18 at. % and approximately 22 at. %, thesecond magnetic layer comprises a Pt content, Pt₂, between approximately14 at. % and approximately 18 at. %, and the third magnetic layercomprises a Pt content, Pt₃, less than approximately 14 at. %, andwherein Pt₁−Pt₂ is less than Pt₂−Pt₃.
 7. The apparatus of claim 1,wherein the first magnetic layer comprises a first granular magneticlayer comprising a first magnetic material and a first oxide, andwherein the second magnetic layer comprises a second granular magneticlayer comprising a second magnetic material and a second oxide.
 8. Theapparatus of claim 1, further comprising a continuous granular compositelayer formed on the third magnetic layer, wherein the continuousgranular composite layer has a magnetic anisotropy field H_(k4), andwherein H_(k4) is greater than H_(k3).
 9. The apparatus of claim 1,further comprising a continuous granular composite layer formed on thethird magnetic layer, wherein the continuous granular composite layerhas a magnetic anisotropy field H_(k4), and wherein H_(k4) is less orapproximately equal to H_(k3).
 10. The apparatus of claim 1, whereinH_(k1) is between approximately 16 kOe and approximately 24 kOe.
 11. Theapparatus of claim 10, wherein H_(k2) is between approximately 12 kOeand approximately 24 kOe.
 12. The apparatus of claim 11, wherein H_(k3)is less than approximately 15 kOe.
 13. The apparatus of claim 1, whereinH_(k1) is between approximately 20 kOe and approximately 22 kOe, whereinH_(k2) is between approximately 17 kO and approximately 20 kOe, andwherein H_(k3) is between approximately 9 kOe and approximately 14 kOe.14. The apparatus of claim 1, wherein at least one of the first magneticlayer, the second magnetic layer, and the third magnetic layer comprisesat least one of a Co alloy, alternating layers of a Co alloy and a Ptalloy, or alternating layers of a Co alloy and a Pd alloy.
 15. Anapparatus comprising: n magnetic layers; and n−1 exchange break layers,wherein n is greater than or equal to three, wherein the n−1 exchangebreak layers alternate with the n magnetic layers in the apparatus, andwherein the n magnetic layers comprise respective magnetic anisotropyfields such that the n magnetic layers have a convex magnetic anisotropyfield gradient.
 16. The apparatus of claim 15, wherein n equals four,wherein a first magnetic layer comprises a first magnetic anisotropyfield H_(k1), wherein a second magnetic layer comprises a secondmagnetic anisotropy field H_(k2), wherein a third magnetic layercomprises a third magnetic anisotropy field H_(k3), wherein a fourthmagnetic layer comprises a fourth magnetic anisotropy field H_(k4),wherein H_(k1)−H_(k2) is less than H_(k2)−H_(k3), and whereinH_(k2)−H_(k3) is less than H_(k3)−H_(k4).
 17. The apparatus of claim 15,wherein a first ratio H_(k2)/H_(k1) is greater than a second ratioH_(k3)/H_(k2), and wherein the second ratio is greater than a thirdratio H_(k4)/H_(k3).
 18. A method of forming a perpendicular magneticrecording layer comprising: forming a first magnetic layer having afirst magnetic anisotropy field, H_(k1); forming a first exchange breaklayer on the first magnetic layer; forming a second magnetic layer onthe first exchange break layer, wherein the second magnetic layer has asecond magnetic anisotropy field, H_(k2); forming a second exchangebreak layer on the second magnetic layer; and forming a third magneticlayer on the second exchange break layer, wherein the third magneticlayer has a third magnetic anisotropy field, H_(k3), and whereinH_(k1)−H₂ is less than H_(k2)−H_(k3).
 19. The method of claim 18,wherein a first ratio H_(k2)/H_(k1) is greater than a second ratioH_(k3)/H_(k2).
 20. The method of claim 19, wherein the first ratio isgreater than approximately 0.6, and wherein the second ratio is lessthan approximately 0.6.